This invention relates to a method and apparatus for manufacturing a bulb with a bead sealing gas, wherein a gas is sealed in a glass bulb so as to seal the glass bulb by melting a bead. More particularly, the present invention relates to an improvement in a gas sealing process.
In a conventional light bulb with a bead sealing gas, as shown in FIG. 1, a glass bulb 1 is combined with a bead mount arranged such that a filament 3 attached to the distal ends of lead wires 2 is located at a predetermined position in the glass bulb 1. The resultant structure is evacuated, and a gas 5 is introduced therein. An opening edge portion of the glass bulb 1 and a bead 4 are heated and melted to seal the glass bulb 1. When the gas 5 is not supplied to the light bulb, a vacuum light bulb is obtained.
A conventional process for fabricating a light bulb with a bead sealing gas will be described with reference to FIG. 2. One end of a glass tube 1' is heated and melted to produce a round sealing end. The glass tube 1' is cut to a predetermined length to prepare the glass bulb 1. A small glass tube 4' is cut to a predetermined length, and the lead wires 2 are inserted through the glass tube 4'. The resultant structure of glass tube 4' and lead wires 2 is heated and melted to constitute a bead stem (bead stem manufacturing step A in FIG. 2). The filament 3 is attached to the distal ends of the lead wires 2 of the bead stem, thereby preparing a bead mount. The diameter r of the bead 4 is smaller than the inner diameter R of the glass bulb 1.
The glass bulb 1 is combined with the bead mount, and a gas is sealed therein in a gas sealing step B. As a result, a light bulb 10 with a bead sealing gas therein is prepared.
FIG. 3 is a diagram for explaining the conventional gas sealing step B of FIG. 2. Referring to FIG. 3, a chamber 11 is provided with a cover 12. When a gas is to be sealed in a glass bulb, a mechanical pressure F acts on the cover 12 to hermetically seal the chamber 11. A carbon heater 13 is supported by electrodes 14A and 14B in the chamber 11 and is connected to a power source 15 and a switch 16 located outside the chamber 11. The heater 13 has a circular recess 13A in the upper surface thereof. A light bulb is to be held in the circular recess 13A. For this purpose, a combination of the glass bulb 1 and the bead mount (the lead wires 2, the filament 3 and the bead 4) is held in the circular recess 13A.
A nitrogen gas circuit including a nitrogen gas tank 17, a pressure control valve 18, a pressure meter 19 and a valve 20 is connected to chamber 11. A sealing gas circuit including a sealing gas tank 21, a pressure control valve 22, a pressure meter 23 and a valve 24, and an evacuating circuit including a vacuum pump 25 and a valve 26 are also connected to the chamber 11. In addition, a leak valve 27, a pressure meter 28 and a vacuum meter 29 for measuring a vacuum pressure in the chamber 11 are connected to the chamber 11. The pressure meter 28 and the vacuum meter 29 are switched over by a selector valve 30.
When the gas is to be sealed in the bulb 1, the glass bulb 1 and the bead mount are set in the recess 13A of the heater 13. The cover 12 is closed and a pressure F is applied to the cover 12. In this state, the vacuum pump 25 is started to evacuate the chamber 11. The valve 26 of the evacuation circuit is closed after evacuation.
Thereafter, the sealing gas for the light bulb is supplied into the chamber 11 at a predetermined pressure from sealing gas tank 21. The sealing gas is also thereby introduced in the glass bulb 1. The switch 16 is turned on to energize the carbon heater 13 to seal the edge portion of the glass bulb 1 with the bead 4. Thus, a light bulb with a bead sealing gas is prepared.
The glass bulb 1 can be sealed with the bead 4 in a sealing gas atmosphere in the chamber 11, so that the lead wires 2 and the filament 3 will not be oxidized.
In the above-described conventional process, an expensive sealing gas is introduced in the entire space inside the chamber 11. Even if a plurality of light bulbs are prepared in a single cycle, the amount of sealing gas per light bulb is high, resulting in high cost. In particular, when the gas pressure is increased, the manufacturing cost is increased.
If a liquid nitrogen cooling method is used in the process for manufacturing a light bulb sealed with a bead, the glass is distorted due to a temperature difference between cooling and heating temperatures for sealing, resulting in cracks. Among gas sealed light bulbs, a light bulb with a butt sealing gas has been proposed. In this known technique, an evacuation pipe is connected to a vacuum pump, and a gas is introduced into the bulb while it is cooled by liquid nitrogen so as to increase a sealing gas temperature. The evacuation portion is then tipped off. However, use of liquid nitrogen results in high cost. The evacuation pipe includes a tip-off portion, so that the overall length of the bulb becomes increased. This increase of length becomes a problem in compact light bulbs.
It is an object of the present invention to provide a method and apparatus for manufacturing a high-efficiency, long-life, lost-cost, high-pressure and compact light bulb (e.g., halogen lamps) with a bead sealing gas.